1. Field of the Invention
The present invention relates to a speed control apparatus for a synchronous reluctance motor, and more particularly to a speed control apparatus for a synchronous reluctance motor which can accurately control the rotating speed of the motor, in accordance with a variation in load, without using any sensor adapted to detect the position of a rotor included in the motor.
2. Description of the Related Art
A synchronous motor, which is a kind of an AC motor, is a constant-speed motor which rotates at a fixed speed, irrespective of the load applied thereto at a certain frequency, that is, at a synchronous speed. In particular, in a synchronous reluctance motor, torque is generated, based on reluctance components. Accordingly, the rotation of the rotor included in the synchronous reluctance motor results from only a reluctance torque.
FIG. 1 is a plan view schematically illustrating a configuration of a conventional three-phase synchronous reluctance motor.
Referring to FIG. 1, the conventional three-phase synchronous reluctance motor, which is denoted by the reference numeral 100, includes a stator 101 adapted to create a rotating magnetic field upon receiving an AC voltage applied thereof, and a rotor 102 arranged inside the stator 101 and adapted to rotate by virtue of the rotating magnetic field created by the stator 101.
As shown in FIG. 2, the rotor 102 is divided into four regions each formed with grooves 102h. The grooves 102h of each rotor region are symmetrical with those of a facing one of the remaining rotor regions. The grooves 10h are adapted to generate an increased difference between a reluctance generated in a d-axis direction and a reluctance generated in a q-axis direction, thereby generating a reluctance torque for rotating the rotor 102. In FIG. 2, the reference numeral 102f denotes a flow of magnetic flux generated by virtue of the magnetic field created by the stator 101.
FIG. 3 is a block diagram schematically illustrating a conventional speed control apparatus applied to a three-phase synchronous reluctance motor having the above-mentioned configuration.
As seen in FIG. 3, the conventional speed control apparatus includes a speed controller 301 for receiving a deviation between a speed command value outputted from a main control unit (not shown) and an actual speed of the three-phase synchronous reluctance motor 310 detected by a rotor position detector 309. The speed controller 301 controls the speed of a rotor 102 included in a synchronous reluctance motor 310 based on the speed deviation. The speed control apparatus also includes a magnetic flux command generator 305 for receiving an output signal from the rotor position detector 309 and computing a magnetic flux angle of the rotor 102 based on the received output signal.
The speed control apparatus also includes a magnetic flux angle operator 307 for receiving an output signal from the rotor position detector 309, thereby computing a magnetic flux angle of the rotor; a coordinate converter 308 for conducting a coordinate conversion of a three-phase current inputted to the synchronous reluctance motor 310 into a two-phase; and a magnetic flux controller 306 for receiving an output signal from the magnetic flux command generator 305 and an output from the coordinate converter 308, thereby controlling a magnetic flux-related current.
The speed control apparatus further includes a current controller 302 for receiving a deviation between an output signal from the speed controller 301 and the output signal from the coordinate converter 308, along with an output signal from the magnetic flux controller 306, thereby generating a torque-related voltage command and a magnetic flux-related command. The speed control apparatus also includes a voltage generator 303 for receiving the torque-related voltage command and magnetic flux-related command outputted from the current controller 302 and the output signal from the magnetic flux angle operator 307, thereby outputting a three-phase voltage command. An inverter 304 receives the three-phase voltage command from the voltage generator 303 and supplies an AC voltage corresponding to the received three-phase voltage command to the three-phase synchronous reluctance motor 310.
In the conventional speed control apparatus having the above-mentioned configuration, the speed controller 301 receives a deviation between a speed command outputted from the main control unit (not shown) and a speed value of the three-phase synchronous reluctance motor 310 fed back from the rotor position detector 309. The speed controller 301 then outputs a current command iqs* relating to a torque in the q-axis direction of a rotating coordinate system, based on the received speed deviation.
The magnetic flux command generator 305 detects a positive torque range and a positive output range from the output signal from the rotor position detector 309, thereby outputting a current command ids* relating to magnetic flux in the d-axis direction of the rotating coordinate system. The magnetic flux controller 306 receives a deviation between the magnetic-flux-related current value ids* outputted from the magnetic flux command generator 305, and a two-phase-converted magnetic-flux-related current value ids outputted from the coordinate converter 308, thereby controlling a magnetic-flux-related current.
The magnetic flux angle operator 307 receives the output signal from the rotor position detector 309, thereby computing a magnetic flux angle {circumflex over (xcex8)} of the rotor. Based on the magnetic flux angle {circumflex over (xcex8)}, the coordinate converter 308 conducts a coordinate conversion for a three-phase current inputted to the synchronous reluctance motor 310 into a two-phase, that is, a q and d-axis phase.
The current controller 302 receives the torque-related current command iqs* and the magnetic-flux-related current command ids*, and generates a torque-related voltage command Vqs* and a magnetic-flux-related voltage command Vds*, respectively. The torque-related voltage Vqs*, and magnetic-flux-related voltage commands Vds*, are applied to the voltage generator 303, which also receives the magnetic flux angle {circumflex over (xcex8)} from the magnetic flux angle operator 307. Based on these received signals, the voltage generator 303 outputs three-phase voltage commands Vas, Vbs, and Vcs. The inverter 304 then applies a corresponding voltage to the synchronous reluctance motor 310 based on the three-phase voltage commands Vas, Vbs, and Vcs.
In a speed control apparatus according to the above-mentioned conventional synchronous reluctance motor, a sensor such as an encoder or a hall IC is used for the rotor position detector 309 and adapted to obtain information about the position of the rotor. However, there are various technical difficulties with an application of such a sensor to refrigerators or air conditioners.
The present invention has been made in view of the above mentioned problems, and an object of the invention is to provide a speed control apparatus for a synchronous reluctance motor which can accurately control the rotating speed of the motor by detecting only the current and voltage of each phase flowing in the motor without using any separate sensor that is necessarily adapted to detect the position of a rotor included in the motor.
These and other objects are accomplished by a speed control apparatus for a synchronous reluctance motor comprising a voltage detector for detecting a voltage applied to the synchronous reluctance motor; a first phase converter for receiving voltages in three phases outputted from the voltage detector based on the voltage detection thereof, and converting the three-phase voltages into equivalent voltages in two phases; a current detector for detecting a current applied to the synchronous reluctance motor; a second phase converter for receiving currents in three phases outputted from the current detector based on the current detection thereof, and converting the three-phase currents into equivalent currents in two phases; and a rotor speed operator for receiving the two-phase voltages outputted from the first phase converter, thereby computing a speed of a rotor included in the synchronous reluctance motor.
These and other objects are further accomplished by a method of controlling operating speed and operating torque for a synchronous reluctance motor, the method comprising the steps of detecting each phase current and each phase voltage of said motor; and controlling rotating speed and torque of said motor based on inductance variations determined from each phase current and each phase voltage of a stator of said motor.
In accordance with the present invention, it is possible to accurately control the rotating speed and torque of the motor by detecting only the current and voltage applied to the motor without using any separate sensor adapted to detect the position of a rotor included in the motor. In order to achieve an enhancement in control accuracy, an inductance calculation is conducted, and an inductance compensation is carried out based on the result of the inductance calculation.
Advantages of the present invention will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the present invention will become apparent to those skilled in the art from this detailed description.